There is a tendency of an increased number of leads in an electronic part to be used in a communication apparatus or an integrated circuit in recent years following rapid communication speed in the communication apparatus or high density of the integrated circuit. Although an electronic part such as quad flat package (QFP) and small outline integrated circuit (SOIC) has existed in the past as an electronic part having the increased number of leads, the past QFP, SOIC and the like are short on the number of leads because any further multifunction has been required in the electronic parts in recent times. A ball grid array (hereinafter referred to as “BGA”) such as plastic ball grid array (PBGA), ceramic ball grid array (CBGA) and tape ball grid array (TBGA) has become used as the electronic parts having an increased number of leads.
However, the ceramic ball grid array (hereinafter, referred to as “CBGA”) to be used in a super computer or the like is heated when applying voltage thereto so that a ceramic board and a printed circuit board (for example, a glass epoxy board or the like) constituting the corresponding CBGA expand based on this heating. When ceasing applying voltage to CBGA, the ceramic board and the glass epoxy board contract. Thus, the ceramic board and the glass epoxy board repeat to expand and contract by applying voltage to CBGA/ceasing applying the voltage to CBGA.
In general, a thermal expansion coefficient of the ceramic board is 8 ppm/° C. and a thermal expansion coefficient of the glass epoxy board is 15-20 ppm/° C. Therefore, thermal stress occurs in the ceramic board and the glass epoxy board arising from any difference between the thermal expansion coefficient of the ceramic board and thermal expansion coefficient of the glass epoxy board. A ceramic column grid array (hereinafter, referred to as “CGA”) in which solder columns having more excellent ability to absorb the thermal stress than that of the solder balls have been used has become used in place of CBGA in recent years.
In the solder columns used in the CGA, linear high-temperature solder that is predominantly composed of lead (Pb), metal line, solder-plating metal line and the like are used. Although, as shapes of the solder columns, there are various kinds thereof following a scale of CGA and numbers of leads, the column-shaped one having a diameter of 0.5 mm and a length of 2.54 mm has been often used. It is necessary for such CGA to mount each of the solder columns at right angles to the ceramic board, in order to enable the solder columns to sufficiently exhibit its ability to absorb the thermal stress.
The following will describe a popular method of forming CGA. Though not shown, first, solder paste is pasted on electrode portions of the ceramic board. Next, a mounting jig for mounting the solder columns at right angles to the corresponding electrode portions is put on the ceramic board. The solder columns are then passed through the through-holes perforated in the mounting jig so that the solder columns stand in the solder paste on the electrode portions. This is inserted into heating device such as a reflow furnace while such a condition being kept, which heats this under a desired temperature condition. As a result thereof, the solder paste pasted on the electrode portions of the ceramic board is melted so that the ceramic board and the solder columns are soldered to each other, thereby forming CGA.
As other methods of mounting the solder columns at right angles to the ceramic board, there are, for example, a method in which the solder columns are mounted using an alignment jig for aligning them in a row as disclosed in Japanese Patent Application Publication No. 2004-221287 and a method in which the solder columns are suctioned directly to a suction head so as to be aligned and the aligned solder columns are mounted on the ceramic board as disclosed in the publication WO2006/48931. Thus, if a shape of each of the solder columns lacks precision, the solder columns cannot be aligned by the alignment jig or they are caught in the alignment jig while aligning them using the alignment jig so that solder columns cannot be mounted. Therefore, the solder columns to be mounted on CGA are required to become the solder columns formed as column shapes, which have a good shape precision and an equal length.
In order to install CGA on the glass epoxy board, first, solder paste is pasted on electrode portions of the glass epoxy board. Next, the solder columns of CGA are mounted on the corresponding electrode portions and then, are heated in heating device such as a reflow furnace. As a result thereof, the solder paste is melted so that the solder columns and the glass epoxy board are soldered to each other, thereby installing CGA on the glass epoxy board.
In such a way, in order to set the solder columns between the ceramic board and the glass epoxy board, the heating twice in the reflow furnace is required. Therefore, the high-temperature solder is used as solder alloy to be used in the solder columns of CGA so that it cannot be melted by the heating twice in the reflow furnace and the heating from IC chip mounted in a super computer or the like.
Further, since the solder columns join the ceramic board and the glass epoxy board, a crack or a breakage may occur in any of the solder columns because of thermal stress if the solder columns are too hard.
Therefore, the high-temperature solder to be used in the solder columns has a Pb based composition such as 95Pb-5Sn and 89.5Pb-10.5Sn. Such Pb based high-temperature solder is softer than that of other metal material and its Mohs hardness is a range of 1.5 through 2.0.
A method of manufacturing the solder column in which linear solder is used and this solder is cut to a desired length is popular. Patent document 1 discloses that after an end of every solder column is soldered to the ceramic board, the other end of the solder column is cut by a knife, a razor or the like so that the solder columns are aligned in height.